Curable pressure sensitive adhesive compositions

ABSTRACT

Curable pressure sensitive adhesive compositions comprising an acrylate copolymer, a mono-acrylate oligomer, a multi-acrylate oligomer having from 2 to 5 acrylate functional groups per molecule, and a photoinitiator, the adhesive exhibiting pressure sensitive adhesive characteristics and forms at least a semi-interpenetrating polymer network when cured; wherein the semi-IPN has an average molecular weight between crosslinks (M c ) greater than about 3000, and the cured adhesive has a peel strength greater than about 40 N/dm. Embodiments of the adhesive compositions, when cured, are optically clear and resistant to heat and moisture.

TECHNICAL FIELD

This invention relates to adhesive compositions, and more particularlyto adhesive compositions that can be both pressure sensitive andcurable.

BACKGROUND

Pressure sensitive adhesives (PSA) have been used in a variety ofapplications, as they provide many desirable characteristics such asremovability and ease of application. For a more permanent and highlysmooth bond, some conventional PSAs may not necessarily have sufficientstrength to hold and maintain its adherence on certain substrates.Furthermore, a conventional PSA when applied to certain materials, maynot be able to withstand exposure to elevated temperatures or highhumidity. For example, application of a PSA on acrylic sheets andpolycarbonate sheets that are known to be “outgassing materials” anddifficult to bond, can result in bubbling and delamination.

Curable adhesives (e.g. heat or light cured) have been used inapplications where substrates require substantial permanency and highstrength adherence. Conventional curable adhesives, however, aretypically not provided as a PSA nor in the form that is easy to apply,such as a tape. For optical product applications (e.g. glazings),curable adhesives have been desirable, as they can provide opticallyclear, strongly adhered laminates (e.g. layered substrates).

To achieve both strength and ease of application, hybrid compositionshave been developed that can be used in optical applications. Forexample, a light curable, polyester based adhesive has been used forplastic glazing applications. In digital video disc (DVD or opticaldiscs) bonding and CRT applications, a liquid adhesive formulation hasbeen used. For bead bonding in making retroreflective articles, acurable polymeric network has been suggested.

Strength and application, however, are not the only criteria that manyoptical substrates/laminates require. Certain optical products areexposed to harsh environmental conditions, such as heat, UV (solar)light, water, etc. For example, vehicle windshields generally exist inoutdoor conditions that submit them to all types of weather. Thesewindshields typically include substrates such as acrylic orpolycarbonate, adhered to a solar or infra-red (IR) reflecting film madefrom a multi-layer optical film (MLOF) (3M Co; St. Paul, Minn.). Thematerials may become optically obstructed if the adhesion between thelayers is damaged or compromised.

What is desired is an adhesive composition that can be used inapplications where optical clarity is needed, as well as ease ofapplication for efficient manufacturing. An adhesive composition whoseintegrity is maintained even when exposed to extreme temperature andmoisture conditions is also desired.

SUMMARY OF THE INVENTION

The invention provides adhesive compositions that can be optically clearand environmentally stable. In certain embodiments, the adhesivecompositions can be applied as a pressure sensitive adhesive (andtherefore removable if desired), and subsequently cured to provide amore permanent bond by forming a secure structural adhesive bond. As aPSA, the composition comprises, among other things, components havingcurable functional groups that can be activated by ultra-violetradiation and other energy sources. Curing can be accomplished via freeradical polymerization, where an interpenetrating polymeric network isformed. Advantageously, UV absorbers can also be present in certainadhesive compositions.

Embodiments of the invention can be optically transmissive in both thecured and uncured state. The compositions can therefore be particularlyuseful in bonding applications that require optical clarity as well assufficient bond strength. Compositions of the invention can also be usedin bonding substrates that are exposed to elevated temperatures andmoisture. Thus, exemplary compositions can be used to laminateout-gassing substrates such as acrylic or polycarbonate sheets, whereresultant laminates can exhibit resistance to bubbles, delamination,haze and whitening.

In one aspect, an adhesive composition includes an acrylate copolymer;acrylated oligomers and an initiator that initiates free radicalpolymerization. The acrylated oligomers component can comprise amono-acrylate oligomer, and a multi-acrylate oligomer having 2 to 5acrylate functionalities per molecule. The blend of all componentsprovide a pressure sensitive adhesive that can be cured, such as by UVirradiation, to form at least a semi-interpenetrating polymer network(IPN) having an average molecular weight between crosslinks (M_(c))greater than about 3000. The cured adhesive can exhibit a peel strengthgreater than about 40 N/dm, as tested according to test methodsdescribed herein.

In another aspect, an adhesive composition is provided that includes anacrylate copolymer; acrylated oligomers; a photoinitiator that initiatesfree radical polymerization; a UV absorber.

In certain aspects, the adhesive is optically transmissive and thereforeuseful in optical element applications. Thus, in another aspect, theinvention provides an optical element that includes at least one opticalsubstrate having a curable pressure sensitive adhesive compositionapplied thereon and another substrate positioned adjacent to theadhesive. Either one or both of the substrates can be an outgassingmaterial.

In a further aspect, a method of using a curable pressure sensitiveadhesive is provided, where the method includes: providing an opticalsubstrate; applying onto a major surface of said optical substrate, anadhesive composition comprising a blended composition of an acrylatecopolymer; a mono-acrylate oligomer; a multi-acrylate oligomer having 2to 5 acrylate functionalities per molecule; and a photoinitiator, thecomposition having pressure sensitive adhesive characteristics;positioning a second substrate adjacent the optical substrate with theadhesive therebetween; and curing the adhesive using actinic energy toform an interpenetrating polymeric network.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DETAILED DESCRIPTION OF EMBODIMENTS

In embodiments of the invention, a composition is provided that includesan acrylate copolymer, a mono-acrylate oligomer, a multi-acrylateoligomer, and an initiator, such as a photoinitiator. The components,when blended, provide an adhesive that can be applied as a pressuresensitive film or tape. Upon exposure to actinic radiation, the appliedblend can then cure to harden to provide a secure, structural bond. Thebond can be optically clear, therefore making the adhesive compositionuseful in optical products (e.g. glazings, laminates, elements, and thelike).

The acrylate copolymer is generally a prepolymerized component, that incertain embodiments, exhibits PSA characteristics. A wide variety ofacrylate copolymers can be used and are known in the polymer andadhesive arts, as are methods of preparing the monomers and polymers.Acrylate copolymers are generally prepared by polymerizing(meth)acrylate monomers, e.g., polymers prepared from one or more(meth)acrylate monomers, optionally with any one or more of a variety ofother useful monomers; where “(meth)acrylate” monomer is used to refercollectively to acrylate and methacrylate monomers. The copolymers canbe present in combination with other, non-(meth)acrylate, e.g.,vinyl-unsaturated, monomers. Suitable acrylate copolymers include, butare not limited to, isooctyl acrylate/methyl acrylate/acrylic acid(IOA/MA/AA) and isooctyl acrylate/acrylic acid (IOA/AA). The acrylatecopolymers can include optional crosslinkers such as, for example,bis-aziridine or multi-functional isocyanates. Specific examples ofacrylate copolymers useful according to the invention include thoseprepared from free radically polymerizable acrylate monomers oroligomers such as described in U.S. Pat. No. 5,252,694 at col. 5, lines35-68.

Examples of useful monomers for the acrylate copolymer include, but notexclusively, the following classes:

Class A—acrylic acid esters of an alkyl alcohol (preferably anon-tertiary alcohol), the alcohol containing from 1 to 14 (preferablyfrom 4 to 14) carbon atoms and include, for example, methyl acrylate,ethyl acrylate, n-butyl acrylate, t-butyl acrylate, hexyl acrylate,isooctyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, isobornylacrylate, phenoxyethyl acrylate, decyl acrylate, and dodecyl acrylate;

Class B—methacrylic acid esters of an alkyl alcohol (preferably anon-tertiary alcohol), the alcohol containing from 1 to 14 (preferablyfrom 4 to 14) carbon atoms and include, for example, methylmethacrylate, ethyl methacrylate, n-propyl methacrylate, n-butylmethacrylate, isobutyl methacrylate and t-butyl methacrylate;

Class C—(meth)acrylic acid monoesters of polyhydroxy alkyl alcohols suchas 1,2-ethanediol, 1,2-propanediol, 1,3-propane diol, the various butyldiols, the various hexanediols, glycerol, such that the resulting estersare referred to as hydroxyalkyl (meth)acrylates;

Class D—multifunctional (meth)acrylate esters such as 1,4-butanedioldiacrylate, 1,6-hexanediol diacrylate, glycerol diacrylate, glyceroltriacrylate, and neopentyl glycol diacrylate although these monomers aregenerally not preferred for reactive extrusion or melt blending;

Class E—macromeric (meth)acrylates such as (meth)acrylate-terminatedstyrene oligomers and (meth)acrylate-terminated polyethers, such as aredescribed in PCT Patent Application WO 84/03837 and European PatentApplication EP 140941;

Class F—(meth)acrylic acids and their salts with alkali metals,including, for example, lithium, sodium, and potassium, and their saltswith alkaline earth metals, including, for example, magnesium, calcium,strontium, and barium.

As used herein and in the claims, a “mono-acrylate oligomer” is definedas an oligomer having only one acrylate functional group. Themono-acrylate can provide the backbone for the polymer which forms uponblending it with an acrylate copolymer and a multi-acrylate oligomer asdescribed herein. A “multi-acrylate oligomer,” as used herein and in theclaims, is intended to signify an oligomer having at least two acrylatefunctional groups. The acrylate functionalities can be terminal groups,or they can be grafted onto a site within the oligomer chain. Uponblending with the other components of the composition, themulti-acrylate oligomer provides the crosslinks or branches needed toform a network with the mono-acrylate oligomer backbone.

The mono-acrylate and mutli-acrylate oligomers are chosen and providedin amounts such that the adhesive composition can have a desirablebalance of cohesive and adhesion strength. In some embodiments, theoligomers are present in amounts to balance such characteristics withoptical clarity and heat/humidity stability as well. The oligomers canbe present in sufficient amounts relative to each other so that thecomposition can achieve and maintain that balance. Insufficient amountsof multi-acrylate oligomer, for example, can result in a lack ofcohesive strength. If an excessive amount of multi-acrylate oligomer isused relative to the mono-acrylate concentration, a resultantcomposition may have too much crosslinking, (e.g. an average molecularweight between crosslinks, M_(c), that is too low), which canconsequently have detrimental effects on the adhesion strength of thecomposition. Exemplary adhesive compositions according to the inventioncan have a M_(c) value greater than about 3000. Depending on the ratioof the amounts of oligomers, and the number of acrylate functionalitiesin the multi-acrylate oligomer (and thereby the molecular weights of thecomponents), certain adhesive compositions can form a semi-IPN having anM_(c) value greater than about 5000.

Compositions according to the invention can have greater amounts ofmono-acrylate oligomer than multi-acrylate oligomer. This aids inproviding an optically clear and stable cured adhesive. In certaincompositions, the ratio of the amounts of mono-acrylate oligomer tomulti-acrylate oligomer is about 1:1. It is contemplated that the ratioof mono- to multi-acrylate oligomer can be 3:1, and can also be up toabout 6:1. This ratio can, of course, be adjusted depending on themolecular weight (and extent of acrylate functionalities) of theacrylated oligomers.

Selection of the acrylate-functionalized oligomers can be based ondesired performance criteria or characteristics of a resulting adhesivecomposition. In one aspect, it can be desired that the composition havepressure sensitive adhesive characteristics for ease of application ontosubstrates, as well as removability when necessary. In another aspect,however, heat and humidity stability can be particularly desirablecharacteristics for the adhesive when it is applied to substratesultimately used for laminates intended for outdoor use or in otherenvironments having elevated temperatures and/or high humidity. Cohesiveand adhesive strength of a cured adhesive composition can therefore bemodified, depending on the resulting interpenetrating polymeric networkthat is achieved by selection of the oligomers.

Suitable mono- and multi-acrylate oligomers for compositions of theinvention can have a glass transition temperature (Tg) of less thanabout 20° C. The acrylate functionalized oligomers useful in theadhesive composition can be represented by structure (I) below:

where R1 is H or CH₃;

R2 is (CH₂)_(m), where m is 0-6;

X is an n-valent radical group such as a polyol linkage or an alkylgroup; and n is greater than or equal to 1.

For structure (I), wherein n is equal to 1, a mono-acrylate oligomer isprovided. When n is greater than 1, a multi-acrylate oligomer isprovided. In certain embodiments of the invention, oligomers areutilized having n being from 1 to 6. Exemplary compositions include amulti-acrylate oligomer comprising from 2 to about 5 acrylatefunctionalities per molecule. In an aspect of the invention, theadhesive composition has a mono-acrylate oligomer (n=1) in combinationwith a diacrylate oligomer (n=2).

In an exemplary composition, the acrylate functionalized oligomers canbe urethane diacrylate oligomers (where Z in structure (I) is —COO, andn=2), represented by structure (II) below:

These oligomers can have a polyol linkage in structure (II) (or “X” asindicated in structure (I) above) that includes, for example, a methanemoiety, a carbonate moiety, an ester moiety, or an ether moiety. Apolyester polyol can be formed by reacting a polybasic acid (e.g.,terephthalic acid or maleic acid) with a polyhydric alcohol (e.g.,ethylene glycol or 1,6-hexanediol). A polyether polyol useful for makingthe acrylate functionalized urethane oligomer can be chosen from, forexample, polyethylene glycol, polypropylene glycol,poly(tetrahydrofuran), poly(2-methyl-tetrahydrofuran),poly(3-methyl-tetrahydrofuran) and the like. Alternatively, the polyollinkage of an acrylated urethane oligomer (structure (II)) can be apolycarbonate polyol.

Acrylate functionalized urethane oligomers can be synthesized, forexample, by reacting a diisocyanate or other polyvalent isocyanatecompound with a polyvalent radical polyol to yield an isocyanateterminated urethane prepolymer. Subsequently, acrylates or methacrylateshaving a hydroxyl group can then be reacted with the terminal isocyanategroups of the prepolymer. Both aromatic and aliphatic isocyanates can beused to react with the urethane to obtain the oligomer. Examples ofdiisocyanates useful for making the acrylated oligomers are 2,4-tolylenediisocyanate, 2,6-tolylene diiscyanate, 1,3-xylylene diisocyanate,1,4-xylylene diisocyanate, 1,6-hexane diisocyanate, isophoronediisocyanate and the like. Examples of hydroxy terminated acrylatesuseful for making the acrylated oligomers include, but are not limitedto, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,4-hydroxybutyl acrylate, polyethylene glycol (meth)acrylate and thelike. A urethane mono-acrylate oligomer comprises one acrylate group andat least one urethane group. Mono-acrylate oligomers can be providedusing commercially available urethane-acrylate oligomers, including, forexample, GENOMER 1122 (Rahn USA Corp.; Aurora, Ill.) and EBECRYL CL 1039(UCB Chemicals; Smyrna, Ga.). A urethane multi-acrylate oligomer can be,for example, any urethane oligomer having at least two acrylatefunctionalities, and in an aspect, less than about six functionalities.Suitable urethane multi-acrylate oligomers are also commerciallyavailable such as, for example, CN962, CN964, CN965, CN934, and CN 972from Sartomer Co. (Exton, Pa.) and ACTILANE 130, 170, 270, and 290 fromAkzo Nobel Resins (Baxley, Ga.) and GENOMER 4269 from Rahn USA Corp.(Aurora, Ill.) and EBECRYL 230, 270, 8803, 4827, and 6700 from UCBChemicals (Smyrna, Ga.).

Alternatively, the acrylate functionalized oligomers can be polyesteracrylate oligomers, acrylated acrylic oligomers, or polyether acrylateoligomers. Suitable acrylate oligomers include, for example,commercially available products such as CN131, an aromatic monoacrylate,and CN132, and aliphatic diacrylate, both of which are available fromSartomer Co. (Exton, Pa.). Useful polyester acrylated oligomers includeCN292, CN2200, and CN2255 from Sartomer Co. (Exton, Pa.) and EBECRYL 81,83, 450, and 2047 from UCB Chemicals (Smyrna, Ga.). Suitable polyetheracrylated oligomers include GENOMER 3497, commercially available fromRahn USA Corp. (Aurora, Ill.) and CN550 from Sartomer Co. (Exton, Pa.).

The acrylate copolymers and the acrylated oligomers can be included inan adhesive composition according to the invention in any relativeamounts that, in combination with the free radical initiator and otheroptional components if present, can result in a useful balance ofadhesive properties (e.g., clarity, optionally, PSA characteristics,peel strength, heat & humidity stability) in both the uncured and curedstates. Particularly useful characteristics are, among others, theoptical clarity and heat/humidity stability the adhesive can exhibit.For the acrylate copolymer, an amount can be included that provides thefunctional properties of a pressure sensitive adhesive, as describedherein and understood in the art.

In embodiments of the invention, the mono-acrylate and multi-acrylateoligomers are present in amounts relative to that of the acrylatecopolymer and the total weight of the composition, that provides adesired combination of pressure sensitive adhesive properties,structural bond properties, optical clarity, and stability of theseproperties over time. In accordance with certain embodiments of theinvention, the acrylated oligomers can be present in the adhesivecomposition at about 20 to about 60 wt. percent of the total adhesivecomposition.

At least one free radical initiator is included in the adhesivecomposition of the invention to initiate the polymerization, and therebyform a structural bond. Free radical initiators, such as photoinitiatorsthat are useful for reacting or polymerizing acrylate materials are wellunderstood, as are their use and the amounts to be included in anadhesive as described herein. Exemplary free radical photoinitiatorsuseful for polymerizing the acrylated oligomers include the benzoinethers, such as benzoin methyl ether or benzoin isopropyl ether,substituted benzoin ethers, such as anisoin methyl ether, substitutedacetophenones, such as 2,2-diethoxyacetophenone and2,2-dimethoxy-2-phenylacetophenone, substituted alpha-ketols, such as2-methyl-2-hydroxypropiophenone, aromatic sulfonyl chlorides, such as2-naphthalene-sulfonyl chloride, and photoactive oximes, such as1-phenyl-1,2-propanedione-2(O-ethoxycarbonyl)oxime. Suitable freeradical photoinitiators for use in the compositions of the invention,include, but are not limited to, commercially available compounds suchas Irgacure 651 and 819 (CIBA Specialty Chemicals Corp.; Tarrytown,N.J.).

The amount of free radical initiator can be sufficient to causepolymerization of the adhesive composition and form asemi-interpenetrating polymer network. In an aspect, the amount ofinitiator can be in the range from a number about 0.01 to about 15 partsby weight free radical initiator for one hundred parts by weight totaladhesive composition, with the range from about 0.1 to about 5 parts byweight being preferred.

Optional components that can be included in adhesive compositions of theinvention include, for example, photosensitizers, grafting agents,crosslinkers, tackifiers, reinforcing agents, and other modifiers (e.g.plasticizers). Photosensitizers can be used to alter the wavelengthsensitivity of a photoinitiator. A grafting agent can be used to causeinter-reaction of the acrylate copolymer and the acrylated oligomers.For example, a grafting agent such as 4-Acryloxy Benzophenone (ABP) cangenerate free radicals on the acrylate copolymer, which can then reactwith (meth)acrylate groups.

A crosslinker can be included in the adhesive in a useful amount thatmay improve properties of the adhesive, such as by crosslinking theacrylate copolymer. Such amounts are generally known in the art and willbe understood by skilled artisans. Exemplary amounts of crosslinker canbe in the range from about 0 to about 10 percent by weight, withpreferred amounts being in the range from about 0.1 to about 5 percentby weight. Amounts outside of this range can also be useful, with aparticular amount of crosslinker for any adhesive composition dependingon a number of various factors including the chemistry of thecrosslinker, the chemistry of the acrylate copolymer and acrylatedoligomers, and the desired properties of the cured and uncured adhesive.Exemplary classes of useful crosslinkers are bis-aziridines andmulti-functional isocyanates.

Optionally, and advantageously, embodiments of the invention can includea hindered amine light stabilizer (HALS). Adding such a stabilizeradvantageously does not detract from the adhesive's ability to be bothpressure sensitive and curable, nor does it detrimentally affect theoptical clarity. Suitable hindered amine stabilizer compounds have beendescribed in U.S. Pat. Nos. 5,668,198; 5,668,199; 5,679,794; 6,166,212;and 6,465,645. A commercially available compound, TINUVIN 123 (CIBASpecialty Chemicals Corp; Tarrytown, N.J.).

A UV absorbing component can optionally be included in the adhesivecomposition of the invention. Such a component can aid the adhesive, andthereby any product made using the adhesive, to provide UV-resistance,particularly radiation in the UV-A range, of less than about 410 nm.Suitable UV absorbers include, but are not limited to a benzotriazole,such as TINUVIN 928 (CIBA Specialty Chemicals Corp; Tarrytown, N.J.), atriazine, such as TINUVIN 1577 (CIBA Specialty Chemicals Corp;Tarrytown, N.J.), a benzophenone, such as UVINUL 3039 (BASF;Ludwigshafen, Germany), a benzoxazinone, such as UV-3638 (Cytec;Charlotte, N.C.), and/or an oxalanilide. Embodiments according to theinvention exhibit properties that are characteristic of pressuresensitive adhesive compositions upon application, but before final cureinto an IPN. Pressure sensitive adhesive (PSA) compositions are wellknown to those skilled in the art to possess properties that include:(a) aggressive and permanent tack; (b) adherence with no more thanfinger pressure; (c) sufficient ability to hold onto an adherend; and(d) sufficient cohesive strength. Certain PSAs can also be removedcleanly from its original target substrate. Materials that have beenfound to function well as PSAs include polymers designed and formulatedto exhibit the requisite viscoelastic properties resulting in a desiredbalance of tack, peel adhesion and shear holding power. In accordancewith embodiments of the invention, blending the acrylate copolymer, themonoacrylate oligomer, and the multi-acrylate oligomer can provide anadhesive composition that exhibits pressure sensitive characteristics.

Upon curing a composition according to the invention with any actinic orother radiation, a semi-interpenetrating polymer network (IPN) can beformed. A semi-IPN is a network having only one crosslinked network;whereas a full IPN can have at least two crosslinked networks. Inaspects according to the invention, the semi-IPN comprises a network ofcrosslinked oligomers. Optionally, but only to the extent thatperformance characteristics are not compromised, a second network ofcrosslinked acrylate copolymers can be present. This second network,therefore characterizes the cured adhesive as a full-IPN.

Certain adhesive compositions according to the invention can beoptically transmissive, (e.g., optically clear) in one or both of itsuncured and cured state. Optical clarity allows the adhesive to be usedin preparing optical elements, such as glazings (e.g. windows,windshields), computer monitor displays, CRTs, anti-reflective films,polarizers and the like. In embodiments of the invention, an adhesivecomposition can maintain its optical transmissivity (e.g. clarity) for auseful period of time under generally normal use conditions as well asin prolonged exposure to normal and extreme conditions. A balance ofdesired characteristics such as clarity, stability, bond strength, andintegrity, can be achieved in an adhesive composition of the inventionby modifying the selection of components or ingredients included in theadhesive, including, for example, the multi-acrylate oligomer (and itsconsitutent monomers), the mono-acrylate oligomer, the acrylatecopolymer and the free radical initiator. Additional but optionalcomponents can be included to balance the performance characteristics,as will be appreciated, including, for example, crosslinkers, graftingagents, photosensitizers, etc., in amounts that will balance and improveproperties of the adhesive.

The adhesive compositions can exhibit desirable levels of opticalclarity. Optical clarity can be measured in various ways, including atest described in ASTM D 1003-95. Exemplary adhesive compositions of theinvention, when tested uncured using such test can exhibit a luminoustransmission greater than about 90%, haze of less than about 2%, andopacity of less than about 1%. Upon curing, the optical clarity ofcertain cured adhesives, tested under similar conditions, exhibitsimilar optical clarity.

When an exemplary adhesive according to the invention is used to produceoptical laminates, products can be stable at 90° C. when tested dry, andstable at 60° C. with 90% relative humidity (RH) for at least one week.Certain formulations can be stable at 80° C. with 90% RH for at leastone week. As used herein “stable” is indicative of an uncompromised bondestablished by the secure structural bond formed by the cured adhesive.

Cured adhesive compositions according to the invention can exhibit“permanent” adhesion to a substrate. In embodiments of the invention, acured adhesive exhibits a peel strength of greater than about 40 N/dm,when measured using tests described in the test methods below. Greaterstrengths can also be achieved by modifying components and theirrespective concentrations, for example, peel strengths greater thanabout 50 N/dm or peel strengths greater than about 60 N/dm.

The adhesives of the invention can be used, for example, to bond avariety of substrate materials, including, but not limited to, polymericmaterials (e.g. polyesters), substantially rigid materials (e.g., somepolycarbonates and acrylics), polymethyl methacrylate, flexible films(e.g. IR reflecting films, MLOFs), brightness-enhancing films, glass,and polarizer films. Many of these materials, particularly those thatexhibit optical clarity or light transmissivity are often used to makeoptical products, such as glazings, photosensors, mirrors, polarizers,security films etc. (hereinafter, materials used for making opticalproducts are referred to as “optical substrates”). Advantageously,because embodiments of the invention can exhibit good optical clarity,the adhesive compositions are particularly useful in bonding a varietyof optical components, optical elements, and optical products.

Optical elements include articles and products that have an opticaleffect or optical application, such as screens for computers or otherdisplays; components of such screens such as polarizing layers,reflective layers, and anti-reflective layers, selectively reflectivelayers such as infra-red reflecting optically clear layers; coatings orfilms for windows which may polarize or reflect; other partially orfully reflective optically transmissive products, etc. Often, opticalelements include one or more different layers of optical substratestypically layers or films that are at least partially opticallytransmissive, reflective, polarizing, or optically clear. An adhesive isused to bond the layers together. Optical substrates can include avariety of different materials, including, for example, polymer, glass,metal or metallized polymer, or combinations thereof. Representativeexamples of polymers include polycarbonate, polyester, polyurethane,polyacrylate, polyvinyl alcohol, polyethylene, polyvinyl chloride,cellulose triacetate and combinations thereof. Any one or more of thesematerials may also provide an intended physical property includingflexibility, rigidity, strength, or support, reflectivity,antireflectivity, polarization, transmissivity (e.g. selective withrespect to different wavelengths), etc.

Characteristic of certain optical substrates, however, is a phenomenonreferred to in the art as “outgassing” or “out-gas releasing.” Forexample, rigid layers such as polycarbonates, polyacrylates, polyesters,etc. tend to be outgassing, particularly when they are provided asrelatively thick components (e.g., in the range of millimeters orcentimeters, as opposed to smaller dimensions). Examples of outgassingmaterials include polycarbonates and polyacrylates such as polymethylmethacrylate, having a thickness in the range from about one or threemillimeters. Outgassing materials can adversely affect the stability,clarity, bond strength, or other performance properties of an adhesive.Bonding layers that include at least one outgassing substrate toproduce, for example, optical laminates, can pose challenges in findinga compatible yet stable and strong adhesive. Applying an incompatibleadhesive to an outgassing material can result in defects such as bubblesor partial to full delamination at the adhesive bond between theoutgassing material and another layer. This can occur particularly whenthe opposing or adjacent layer (to the outgassing material) exhibits lowvapor transmissivity, such that any released gas is inhibited orprohibited from passing through. The low vapor transmissive material canact as a barrier to the gas, resulting in the gas collecting at theadhesive interface and causing bubbling, delamination, reduced bondstrength, or loss of clarity. Advantageously, adhesive compositions ofthe invention can be used in these and other applications. Embodimentsof the invention offer improved bond strength and stability and cantherefore reduce or eliminate such bubbling or delamination even wherethe adhesive is used to bond an outgassing layer to a low moisture vaportransmissive layer.

The threshold level of moisture vapor transmissivity that can causeadhesive bonds to be compromised can depend on various factors such asthe composition of the outgassing material, the amount of gas itproduces, conditions of use, and the composition and overall strength,integrity, and stability of an adhesive. In an aspect, films that have amoisture vapor transmission rate of about 30 grams per (meter squared×24hours) or less can be considered a low moisture vapor transmissivematerial (as measured by ASTM E96-80). However, determining whether ornot such a material will cause an unstable adhesive bond, bubbling,delamination, or loss of clarity, will depend on factors such as theadhesive composition and the adjacent substrate to which it is bonded.Examples of low moisture vapor transmission rate films includemetallized films used for their antireflective or conductive properties(for example for EMI shielding) in optical elements. Metallized filmsinclude films such as polyethylene terephthalate (PET) or otherpolymeric materials that include a surface that is partially or fullycoated with a metal or metallic material. One such polyethyleneterephthalate film, is ICI 617, a 127 μm thick film from ImperialChemical Industries Films (Hopewell, Va.). Other examples of metallizedfilms include multilayer AR (antireflective) film such as described inU.S. Pat. No. 6,277,485 columns 13 and 14; and microlayer films such asthose described in U.S. Pat. No. 6,049,419.

Polarizers, generally known to be heat and humidity sensitive materials,can also be bonded using an adhesive composition of the invention. Thesematerials, such as one often referred to industry as a “KE polarizer”are often provided as very thin films. Due to their thinness, thesefilms can shrink when exposed to a certain minimum temperature andhumidity. By applying and curing an adhesive composition of theinvention, a resultant IPN is thereby provided to offer strength to thefilm.

The invention further relates to methods of using the curable PSAadhesives. The curable adhesive compositions may be applied by anyconventional application method, including but not limited to gravurecoating, curtain coating, slot coating, spin coating, screen coating,transfer coating, brush or roller coating, and the like. The thicknessof a coated adhesive layer, (sometimes provided in liquid form), priorto curing, can be any thickness that results in the desired properties,as is well understood in the art. Exemplary thicknesses of an uncured,curable adhesive layer may be in the range from about 0.05 to about 125micrometers.

The amount of cure time to harden or cure the adhesive can vary,depending on a variety of factors, such as the components present in theadhesive composition, the substrates used, as well as the thickness ofthe applied layer. Use of a UV irradiation source can significantlylower the cure time necessary to cure adhesives of the invention,compared to, for example, thermal (heat) curing techniques. Thus,practicing a method according to the invention can provide fastermanufacturing processes, and can lead to decreased operating costs.

In an aspect, an adhesive composition can be applied onto a surface of asubstrate, contacting the curable adhesive with another material, andthen curing the adhesive composition. Lamination can be used to contactthe two materials, having the adhesive therebetween. Optionally, methodscan also include applying the adhesive onto a release liner; drying anysolvent in the adhesive; laminating; polymerizing or curing the acrylateoligomers and optionally acrylate copolymers; and any other steps,techniques, or methods known to be used in the preparation ofmulti-layer articles.

In some optical applications, optical films are laminated onto otheroptical substrates, and subsequently, portions of the optical films needto be cut and then cleanly removed to make special patterns. Adhesivesof the invention can be quite useful in these types of applications, asthe adhesives as well as unwanted film portions (e.g. weed) can becleanly removed in the first stage prior to energy beam cure (e.g. UVirradiation). Once the optical film patterns and designs are set, thenenergy can subsequently be applied to cure and harden the adhesive, toprovide a secure and stable bond.

Preparing the adhesive compositions can be conducted using any of thenumerous conventional methods for combining, blending, and optionallyreacting (meth)acrylate materials, acrylate copolymers, acrylatedoligomers, initiators, and any adjuvants. See for example, U.S. Pat.Nos. 5,252,694, 5,897,727, and 6,180,200. Generally, acrylate copolymermaterials such as those described above can be directly combined withthe described acrylated oligomers and other components of a curableadhesive composition, including crosslinkers, initiators, etc., inamounts as useful and as described herein. While solventless embodimentsare visualized within the scope of this invention, it is contemplatedthat solvents can be used to prepare embodiments of the adhesivecompositions. Representative solvents can be organic, and includeacetone, methyl-ethyl-ketone, ethyl acetate, heptane, toluene,cyclopentanone, methyl cellosolve acetate, methylene chloride,nitromethane, methyl formate, gamma-butyrolactone, propylene carbonate,and 1,2-dimethoxyethane (glyme).

If a photoinitiator is used, irradiation sources that provide energy(e.g., light) in the region from 200 to 800 nm can be used to cureembodiments of the adhesive composition. In an aspect, a useful regionof light is about 250 to about 700 nm. Suitable sources of radiation toinitiate actinic curing include mercury vapor discharge lamps, carbonarcs, quartz halogen lamps, tungsten lamps, xenon lamps, fluorescentlamps, lasers, sunlight, etc. The amount of radiation exposure to effectpolymerization can depend on factors such as the identity andconcentrations of particular free radically polymerizable oligomers, thethickness of the exposed material, the type of substrate(s), theintensity of the radiation source and the amount of heat associated withthe radiation. Alternatively, other sources of energy such as e-beam andgamma ray can be used for curing the adhesive, with or without an addedinitiator.

EXAMPLES

These examples are merely for illustrative purposes only and are notmeant to be limiting on the scope of the invention. All parts,percentages, ratios, etc. in the examples are by weight unless indicatedotherwise.

Table of Abbreviations AA Acrylic Acid BA n-Butyl Acrylate CGL 139Benzotriazole UV absorber (CIBA Specialty Chemicals Corp; Tarrytown, NJ)CN131 Mono-acrylate oligomer from Sartomer with a Tg of 4° C. CN135Mono-acrylate oligomer from Sartomer with a Tg of 20° C. CN137Mono-acrylate oligomer from Sartomer with a Tg of 40° C. CN964 Urethanediacrylate oligomer from Sartomer, used as a 33% solution in ethylacetate EBECRYL CL 1039 Urethane mono-acrylate oligomer (UCB Chemicals;Smyrna, GA) EtOAc Ethyl Acetate Glass Microscope Slides 75 millimeter ×50 millimeter × 1 millimeter Corning No. 2947 Microslides (Corning GlassWorks; Corning, NY) IOA Isooctyl acrylate IR Film Multilayer IRreflecting film comprises alternating layers of PET (A-layer) andco-PMMA (B-layer). These layers are arranged in 6 layer optical repeatunits: 7A, 1B, 1A, 7B, 1A, 1B with 96 such optical repeat units for atotal of 576 layers. This film reflects light in the infraredwave-length region between about 900-1300 nm while allowing lighttransmission in the visible region between 380-770 nm. IRGACURE 819Photo curing agent, (CIBA) MA Methyl Acrylate MELAK Melamine crosslinkedpolyacrylate primer PF Film Multi-layer optical photosensor film of 96.5micrometer thickness (3 M Co.; St. Paul, MN) PC Sheets of polycarbonateof 3 mm thickness (Bayer-Sheffield Plastics Inc.; Sheffield, MA) PETPolyethylene terephthalate PET Film ICI 617 127 micrometer thick PETfilm (Imperial Chemical Industries Films; Hopewell, VA) PMMA Sheets ofpolymethylmethacrylate of 3 mm thickness PSA-1 A solvent based PSAprepared according to conventional radical thermal polymerizationprocedure using the monomers IOA/MA/AA in the ratio 57.5/35/7.5, used asa 26% solids solution in ethyl acetate/toluene. PSA-2 A solvent basedPSA prepared according to conventional radical thermal polymerizationprocedure using the monomers IOA/AA in the ratio 81/19, used as a 19%solids solution in ethyl acetate/toluene. RH Relative Humidity T-10Release Liner CP Film T-10 silicone release coating on 51 micrometer PETfilm (CP Film; Martinsville, VA) T-30 Release Liner CP Film T-30silicone release coating on 51 micrometer PET film (CP Film;Martinsville, VA) TINUVIN 123 Hindered Amine Light Stabilizer (CIBASpecialty Chemicals Corp.; Tarrytown, NJ) Xlinker Bis-aziridinecrosslinker in 5 wt % solution, described in U.S. Pat. Nos. 5,874,143column 4, line 49.Test MethodsAccelerated Aging Test

Accelerated aging tests were conducted at three different conditions:90° C.; 60° C./90% RH and 80° C./90% RH. The aging test results aredetermined by visual observation and reported as either “Pass” if thesample retains its optical clarity and no other defects formed duringthe aging test, or “Fail” if bubbles are present in the adhesive bondline or if delamination occurred at the adhesive bond line.

Optical Property Measurements

Luminous Transmittance and Haze

The luminous transmittance and haze of all samples were measured byusing a TCS Plus Spectrophotometer from BYK-Gardner Inc.; SilverSprings, Md. Haze and opacity values are given for both illuminant Cwith CIE 2° standard observer (C2°) and illuminant A with CIE 2°standard observer (A2°). Sample preparation details are described in thetext.

Opacity Measurement

The same samples used for haze and luminous transmittance measurementswere used for opacity measurement. The BYK Gardner TCS PlusSpectrophotometer was used for opacity measurement, with the standardsize reflectance port (25 mm) installed, and diffuse reflectance(specular excluded) was measured.

180° Peel Adhesion

This peel adhesion test is similar to the test method described in ASTMD 3330-90. Adhesive laminates with dimensions of 2.54 centimeters by 15centimeters were adhered to a IMASS slip/peel tester (Model 3M90 orSP-2000, commercially available from Instrumentors Inc., Strongsville,Ohio). The bonded assembly dwelled at room temperature for about oneminute and was tested for 180° peel adhesion at a rate of 0.30meters/minute (12 inches/minute) over a five second data collectiontime. Two samples were tested; the reported peel adhesion value is anaverage of the peel adhesion value from each of the two samples.

90° Peel Adhesion

The peel force was measured using an INSTRON tensile tester(commercially available from Instron Corp.; Canton, Mass.) at a peelangle of 90 degrees and a peel rate of 0.30 meters/minute (12inches/minute).

Examples 1-4

Adhesive Preparation

In a brown glass reaction vessel was placed IRGACURE 819 and EtOAc inthe amounts shown in Table 1. Once dissolved, the remaining componentsshown in Table 1 were added and the resulting mixture was mixed well toyield an adhesive mixture with 30 weight % acrylated oligomer content.

TABLE 1 IRGACURE EBECRYL CN964 EtOAc 819 CL 1039 Xlinker Example (gram)(gram) (mg) PSA-1 (gram) (gram) (mg, wt %) 1 1.75 5 172 20 1.733 1040.1% 2 1.75 5 172 20 1.733 208 0.2% 3 1.75 5 172 20 1.733 312 0.3% 41.75 5 172 20 1.733 416 0.4%Laminate Preparation

The adhesive solutions described above were coated onto the MELAK primedside of an IR Film, dried at 70° C. for 10 minutes to yield a 37.5 μmthick dry PSA tape. Samples of this PSA tape were laminated ontoPolycarbonate Sheets and PMMA Sheets. After 24 hour dwell, theselaminates were irradiated (through the IR Film) with a Fusion UV CuringSystem at the following conditions for a total UVA (320-390 nm) dose ofabout 2 J/cm²: Fusion “D” bulb, 300 Watts/Inch, 25 feet/minute, 2passes. After irradiation, these samples were stored at ambienttemperature for at least 24 hours before any aging test was carried out.

Aging Test

The above prepared laminates of IR Film/Adhesive/PC Sheet and IRFilm/Adhesive/PMMA Sheet were tested at 90° C. and 60° C./90% RHconditions using the test method described above. Aging tests conductedfor 1 week at each of the test conditions resulted in a “PASS” score forall samples of Examples 1-4.

Peel Adhesion

180° peel adhesion testing was carried out using the test methoddescribed above on the above prepared laminates. The results are shownin Table 2.

TABLE 2 Average 180° Peel of Average 180° Peel of IR Film/Adhesive/PMMAIR Film/Adhesive/PC cured laminate cured laminate Example Adhesive(N/dm) (N/dm) 1 80.8 129.8 2 76.7 87.6 3 79.6 81.8 4 120.6 109.6

Example 5

The adhesive solution prepared in Example 1 was coated onto the MELAKprimed side of an IR Film, dried at 70° C. for 10 minutes to yield a37.5 μm thick dry PSA tape. This PSA tape was then UV cured (Fusion “D”bulb, 300 Watts/Inch, 25 feet/minute, 2 passes), and heat laminated ontoPMMA Sheets using the following procedure: place both PSA tape and PMMASheets in a 85° C. oven for two minutes, and then hand laminate PSA tapeonto PMMA sheets with a rubber roller. After 24 hours dwell, theselaminates passed 1-week aging test at 90° C. and 60° C./90% RHconditions.

Examples 6-9

Adhesive Preparation

In a brown glass reaction vessel were placed the components shown inTable 3 and the resulting mixture was mixed well.

TABLE 3 Wt % acrylate IRGACURE EBECRYL oligomers CN964 819 CGL 139 CL1039 Example (%) (gram) (mg) (mg) PSA-2 (gram) (gram) 6 35 2.12 172 16027.37 2.1 7 40 2.62 172 173 27.37 2.6 8 45 3.22 172 189 27.37 3.2 9 503.94 172 208 27.37 3.9Laminate Preparation

Laminates were prepared as described for Examples 1-4.

Aging Test

The above prepared laminates of IR Film/Adhesive/PC Sheet and IRFilm/Adhesive/PMMA Sheet were tested at 90° C. and 60° C./90% RHconditions using the test method described above. Aging tests conductedfor 42 days at each of the test conditions resulted in a “PASS” scorefor all samples of Example Adhesives 6-9.

Examples 10-15

Adhesive Preparation

In a brown glass reaction vessel were placed the components shown inTable 4 and the resulting mixture was mixed well.

TABLE 4 IRGACURE CGL 139 EBECRYL TINUVIN CN964 819 (mg) CL 1039 123Example (gram) (mg) (wt %) PSA-2 (gram) (gram) (mg) 10 2.63 172 17327.37 2.6 0 2% 11 2.63 172 346 27.37 2.6 0 4% 12 2.63 172 519 27.37 2.60 6% 13 2.63 172 173 27.37 2.6 430 2% 14 2.63 172 346 27.37 2.6 430 4%15 2.63 172 519 27.37 2.6 430 6%Laminate Preparation

Laminates were prepared as described for Examples 1-4.

Aging Test

The above prepared IR Film/Adhesive/PC Sheet and IR Film/Adhesive/PMMASheet were tested at 90° C. and 60° C./90% RH conditions using the testmethod described above. Aging tests conducted for 30 days at each of thetest conditions resulted in a “PASS” score for all samples of Examples10-15.

Examples 16-21 and Comparative Examples C1-C3

Adhesive Preparation

In a brown glass reaction vessel were placed the components shown inTable 5 and the resulting mixture was mixed well.

TABLE 5 Wt % IRGACURE EBECRYL Acrylated CN964 819 PSA-2 CL 1039 ExampleOligomers (gram) (mg) (gram) (gram) C1 0 0 0 27.37 0 C2 10 0.44 17227.37 0.43 C3 15 0.70 172 27.37 0.69 16 20 0.98 172 27.37 0.98 17 251.31 172 27.37 1.3 18 35 2.12 172 27.37 2.1 19 40 2.63 172 27.37 2.6 2045 3.22 172 27.37 3.2 21 50 3.94 172 27.37 3.9Laminate Preparation

Laminates were prepared as described for Examples 1-4.

Aging Test

The above prepared IR Film/Adhesive/PC Sheet and IR Film/Adhesive/PMMASheet were tested at 90° C. and 60° C./90% RH conditions using the testmethod described above. The results are presented in Tables 6-8.

TABLE 6 Example Adhesive in IR Aging Test Conditions Film/Adhesive/PMMALaminate (90° C. for 54 days) C2 Fail C3 Fail 16 Pass 17 Pass

TABLE 7 Example Adhesive in IR Aging Test Conditions Film/Adhesive/PMMAAging Test Conditions (60° C./90% Laminate (90° C. for 34 days) RH for34 days) C1 Fail Fail 18 Pass Pass 19 Pass Pass 20 Pass Pass 21 PassPass

TABLE 8 Example Adhesive in IR Aging Test Conditions Film/Adhesive/PCAging Test Conditions (60° C./90% RH Laminate (90° C. for 34 days) for34 days) C1 Fail Fail 18 Pass Pass 19 Pass Pass 20 Pass Pass 21 PassPass

Example 22

Adhesive Preparation

The components shown in Table 9 were placed in a brown glass reactionvessel and the resulting mixture was mixed well.

TABLE 9 Wt % IRGACURE EBECRYL acrylated CN964 819 PSA-2 CL 1039 Exampleoligomers (gram) (mg) (gram) (gram) 22 30 1.75 172 27.37 1.73Optical Measurements

Laminates of the adhesive prepared above were prepared as described inExamples 1-4 except Glass Microscope Slides were used instead of PMMA orPC. The optical properties were measured using the test methodsdescribed above. The results are shown in Table 10. Referenceinformation for the Glass Microscope Slides, IR Film with MELAK Primerare also included.

TABLE 10 Haze % Opacity % Sample T % C2°/A2° C2°/A2° Glass MicroscopeSlides 92.3 0.5/0.5 0.3/0.3 IR Film/MELAK Primer 89.5 0.7/0.7 0.7/0.7 IRFilm/Adhesive Example 22/Glass; 86.1 1.1/1.1 0.5/0.5 before UV treatmentIR Film/Adhesive Example 22/Glass; 88.68 1.0/1.0 0.5/0.5 after UVtreatment *IR Film/Adhesive Example 22/Glass; 93.2 N/A N/A before UVtreatment *IR Film/Adhesive Example 22/Glass; 96.0 N/A N/A after UVtreatment *samples were measured using glass to calibrate, i.e. T % ofglass = 100%.Laminate Preparation

Laminates of PF/adhesive/PF were prepared using the procedure describedfor Examples 1-4 except that PF substrates were used in place of IR Filmand PC or PMMA.

Aging Test

The above prepared PF/Adhesive/PF Sheet was tested at 90° C., 60° C./90%RH, and 80° C./90% RH conditions using the test method described above.Aging tests conducted for 30 days at each of the test conditionsresulted in a “PASS” score for the Adhesive Example 22.

Peel Adhesion

90° peel adhesion samples were prepared by coating the adhesive ontoT-30 Release Liner, drying at 70° C. for 10 minutes, and furtherlaminated with another T-10 Release Liner to yield a transfer PSA of 114micrometer in PSA thickness. This transfer PSA was laminated ontoanodized Aluminum foil backing film, and further laminated onto a glasssubstrate. The 90° peel testing was carried out using the test methoddescribed above. When the laminate was made with zero dwell time priorto light activation, the peel strength was determined to be 70.0 N/dm.When the laminate had been allowed to dwell overnight before lightactivation, the peel strength as determined to be 105.0 N/dm.

Examples 23-26 and Comparative Example C4

Adhesive Preparation

In a brown glass reaction vessel were placed the components shown inTable 11 and the resulting mixture was mixed well.

TABLE 11 Wt % IRGACURE acrylated CN964 819 PSA-2 CN131 Example oligomers(gram) (mg) (gram) (gram) C4 10 0.44 172 27.37 0.43 23 20 0.98 172 27.370.98 24 30 1.75 172 27.37 1.7 25 40 2.62 172 27.37 2.6 26 50 3.94 17227.37 3.9Laminate Preparation

Laminates were prepared as described for Examples 1-4.

Aging Test

The above prepared IR Film/Adhesive/PC Sheet and IR Film/Adhesive/PMMASheet were tested at 90° C., 60° C./90% RH, and 80° C./90% RH conditionsusing the test method described above. The results are presented inTables 12-13.

TABLE 12 Example Aging Test Aging Test Aging Test Adhesive in IRConditions Conditions Conditions Film/Adhesive/PMMA (90° C. (60° C./90%RH (80° C./90% Laminate for 30 days) for 30 days) RH for 7 days) C4 FailFail Fail 23 Pass Pass Pass 24 Pass Pass Pass 25 Pass Pass Pass 26 PassPass Pass

TABLE 13 Example Aging Aging Test Aging Test Adhesive in IR TestConditions Conditions Conditions Film/Adhesive/PC (90° C. for (60°C./90% (80° C./90% Laminate 30 days) RH for 30 days) RH for 7 days) C4Fail Fail Fail 23 Pass Pass Pass 24 Pass Pass Pass 25 Pass Pass Pass 26Pass Pass PassOptical Measurements

Optical properties of the laminates of the IR Film/adhesive/PC preparedabove were measured using the test methods described above. The resultsare shown in Table 14.

TABLE 14 Weight % Acrylated Haze % Opacity % Example Oligomers T %*C2°/A2° C2°/A2° C4 10 97.04 1.4/1.4 1.0/1.0 23 20 97.19 1.4/1.4 1.0/1.024 30 95.58 1.6/1.5 1.0/1.0 25 40 91.52 3.7/3.3 1.8/1.7 26 50 87.1415.5/14.2 3.8/3.6 *samples were measured using PC to calibrate, i.e. T %of PC = 100%.

Comparative Examples C5-C9

Adhesive Preparation

In a brown glass reaction vessel were placed the components shown inTable 15 and the resulting mixture was mixed well.

TABLE 15 Wt % acrylated CN964 IRGACURE PSA-2 CN135 Example oligomers(gram) 819 (mg) (gram) (gram) C5 10 0.44 172 27.37 0.43 C6 20 0.98 17227.37 0.98 C7 30 1.75 172 27.37 1.7 C8 40 2.62 172 27.37 2.6 C9 50 3.94172 27.37 3.9Laminate Preparation

Laminates were prepared as described for Examples 1-4.

Aging Test

The above prepared IR Film/Adhesive/PC Sheet and IR Film/Adhesive/PMMASheet were tested at 90° C., 60° C./90% RH, and 80° C./90% RH conditionsusing the test method described above. The results are presented inTables 16-17.

TABLE 16 Aging Test Aging Test Aging Test Example Adhesive in IRConditions Conditions Conditions Film/Adhesive/PMMA (90° C. (60° C./90%(80° C./90% Laminate for 7 days) RH for 7 days) RH for 7 days) C5 FailFail Fail C6 Fail Fail Fail C7 Pass Pass Fail C8 Pass Pass Fail C9 FailPass Fail

TABLE 17 Aging Test Aging Test Aging Test Example Adhesive in ConditionsConditions Conditions IR Film/Adhesive/PC (90° C. (60° C./90% (80°C./90% Laminate for 7 days) RH for 7 days) RH for 7 days) C5 Fail FailFail C6 Fail Fail Fail C7 Fail Fail Fail C8 Fail Fail Fail C9 Fail FailFailOptical Measurements

Optical properties of the laminates of the IR Film/adhesive/PMMAprepared above were measured using the test methods described above. Theresults are shown in Table 18.

TABLE 18 Weight % Acrylated Haze % Opacity % Example oligomers T %*C2°/A2° C2°/A2° C5 10 91.9 5.4/5.2 1.8/1.7 C6 20 88.5 16.2/15.2 2.7/2.6C7 30 88.9 38.0/36.1 4.1/3.9 C8 40 87.4 45.8/43.3 4.5/4.4 C9 50 78.747.8/46.5 5.2/5.0 *samples were measured using PMMA to calibrate, i.e. T% of PMMA = 100%.

Comparative Examples C10-C14

Adhesive Preparation

In a brown glass reaction vessel were placed the components shown inTable 19 and the resulting mixture was mixed well.

TABLE 19 Wt % IRGACURE Acrylated CN964 819 PSA-2 CN137 Example oligomers(gram) (mg) (gram) (gram) C10 10 0.44 172 27.37 0.43 C11 20 0.98 17227.37 0.98 C12 30 1.75 172 27.37 1.7 C13 40 2.62 172 27.37 2.6 C14 503.94 172 27.37 3.9Laminate Preparation

Laminates were prepared as described for Examples 1-4.

Aging Test

The above prepared IR Film/Adhesive/PC Sheet and IR Film/Adhesive/PMMASheet were tested at 90° C., 60° C./90% RH, and 80° C./90% RH conditionsusing the test method described above. The results are presented inTables 20-21.

TABLE 20 Aging Test Aging Test Aging Test Example Adhesive in IRConditions Conditions Conditions Film/Adhesive/PMMA (90° C. (60° C./90%(80° C./90% Laminate for 7 days) RH for 7 days) RH for 7 days) C10 FailFail Fail C11 Pass Fail Fail C12 Pass Fail Fail C13 Fail Fail Fail C14Fail Fail Fail

TABLE 21 Aging Test Aging Test Aging Test Example Adhesive in ConditionsConditions Conditions IR Film/Adhesive/PC (90° C. (60° C./90% (80°C./90% RH Laminate for 7 days) RH for 7 days) for 7 days) C10 Fail FailFail C11 Fail Fail Fail C12 Fail Fail Fail C13 Fail Fail Fail C14 FailFail FailOptical Measurements

Optical properties of the laminates of the IR Film/adhesive/PMMAprepared above were measured using the test methods described above. Theresults are shown in Table 22.

TABLE 22 Weight % Acrylated Haze % Opacity % Example Oligomers T %*C2°/A2° C2°/A2° C10 10 91.6 10.4/9.7  2.3/2.3 C11 20 90.9 19.1/18.12.5/2.4 C12 30 91.5 29.6/28.1 3.0/3.0 C13 40 90.8 41.4/39.4 3.7/3.6 C1450 88.4 44.3/42.6 4.3/4.3 *samples were measured using PMMA tocalibrate, i.e. T % of PMMA = 100%.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

1. An adhesive composition comprising: an acrylate copolymer; amono-acrylate oligomer; a multi-acrylate oligomer having 2 to 5 acrylatefunctionalities; and a photoinitiator that initiates free radicalpolymerization; wherein said mono-acrylate oligomer is present in anamount greater than the amount of said multi-acrylate oligomer, andwherein said mono-acrylate oligomer, multi-acrylate oligomer andphotoinitiator, when blended with said acrylate copolymer, forms apressure sensitive adhesive, and when cured, forms a cured adhesivecomprising at least a semi-interpenetrating polymer network having anaverage molecular weight between crosslinks (M_(c)) greater than about3000, said cured adhesive having a peel strength greater than about 40N/dm.
 2. The composition of claim 1, wherein the mono-acrylate oligomerhas a T_(g) of less than about 20° C.
 3. The composition of claim 1wherein the multi-acrylate oligomer has a T_(g) of less than about 20°C.
 4. The composition of claim 1 wherein at least one of themono-acrylate oligomer and the multi-acrylate oligomer is selected froma group consisting of a urethane acrylate oligomer; polyester acrylateoligomer; and a polyether acrylate oligomer.
 5. The composition of claim1 wherein at least one of the mono-acrylate oligomer and themulti-acrylate oligomer comprises urethane acrylate oligomer.
 6. Thecomposition of claim 1 further comprising a UV absorber.
 7. Thecomposition of claim 6 wherein said UV absorber is capable of absorbingradiation having a wavelength less than about 410 nm.
 8. The compositionof claim 1 wherein the adhesive composition, when cured, has an opticaltransmissivity greater than about 90%.
 9. The composition of claim 1,further comprising a crosslinker reactive with said acrylate copolymer.10. The composition of claim 1, further comprising a hindered aminelight stabilizer.
 11. The composition of claim 1, wherein the ratio ofthe amount of mono-acrylate oligomer to multi-acrylate oligomer is about3:1.
 12. The composition of claim 1, wherein the ratio of the amount ofmono-acrylate oligomer to multi-acrylate oligomer is about 6:1.
 13. Thecomposition of claim 1, wherein said composition is UV-curable.
 14. Thecomposition of claim 1, wherein said mono-acrylate oligomer and saidmulti-acrylate oligomer are present in the composition at greater thanabout 20 wt. percent of the total weight of the composition.
 15. Thecomposition of claim 14, wherein said mono-acrylate oligomer and saidmulti-acrylate oligomer are present in the composition at less thanabout 60 wt. percent of the total weight of the composition.
 16. Acurable adhesive composition comprising: an acrylate copolymer; amono-acrylate oligomer; a multi-acrylate oligomer having 2 to 5 acrylatefunctionalities; an ultra-violet light absorber; and a photoinitiatorthat initiates free radical polymerization; wherein said mono-acrylateoligomer is present in an amount greater than the amount of saidmulti-acrylate oligomer; said mono-acrylate oligomer, multi-acrylateoligomer and photoinitiator, when blended with said acrylate copolymer,forms a pressure sensitive adhesive; and said blend of oligomers andcopolymer, when actinically cured, forms a cured adhesive comprising atleast a semi-interpenetrating polymer network with an average molecularweight between crosslinks (M_(c)) greater than about 3000; said curedadhesive exhibiting substantial optical clarity, ultra-violet lightabsorbing capability, and a peel strength greater than about 40 N/dm.17. The composition of claim 16, further comprising a hindered aminelight stabilizer.
 18. The composition of claim 16, wherein the ratio ofthe amount of mono-acrylate oligomer to multi-acrylate oligomer is about3:1.
 19. The composition of claim 16, wherein the ratio of the amount ofmono-acrylate oligomer to multi-acrylate oligomer is about 6:1.
 20. Thecomposition of claim 16, wherein at least one of said mono-acrylateoligomer and multi-acrylate oligomer comprises urethane acrylateoligomer.
 21. The composition of claim 16, wherein at least one of saidmono-acrylate oligomer and multi-acrylate oligomer has a T_(g) less thanabout 20° C.